High pressure fuel injection systems typically include positive displacement pumps such as a swash plate pump or cam ring piston pump to provide highly pressurized fuel (e.g., 30-150 bar system pressure) to fuel injectors in an engine. The positive displacement pump or high pressure pump is mechanically coupled to the engine via a belt, gear, or clutch drive which turns the pump at a ratio of the engine speed. Thus, the performance of the high pressure pump is dependent on the speed of cranking, rotating, or turning of the engine.
Generally, the high pressure pump, which is driven by the engine, is not able to provide full or operating pressure at its output until the engine has been started. Providing the fuel at the operating pressure is necessary for the fuel injectors in the high pressure fuel system to provide proper atomization and high delivery rates.
High pressure fuel systems are typically equipped with a feed pump or conventional low pressure pump in the fuel tank which supplies the fuel to the high pressure pump in the engine compartment. The output of the low pressure pump is generally coupled to the input of the high pressure pump. The low pressure pumps are often electric pumps such as a vane pump, turbine pump, or roller pump and cannot create high system pressures required for atomization and high delivery rates. However, these pumps are able to relatively quickly provide low pressure fuel from the tank independent of engine revolutions.
The low pressure pumps provide the fuel at the specified low pressure as soon as the electrical system of the vehicle or other engine system is turned on. Generally, fuel cannot be directly provided by the low pressure pump through the high pressure pump to the engine because restrictive clearances in the pistons of the high pressure pump prevent fuel flow through the high pressure pump. Heretofore, starting an engine equipped with a high pressure pump is an objectionably slow process because the high pressure pump is not able to provide the fuel until the engine has been started, or cranked (e.g., turned over) a significant number of times.
Another problem associated with high pressure pumps involves the generation of extremely high output pressures when the high pressure pump is deadheaded, such as when the high pressure fuel system becomes a closed system due to a system failure. If the regulator or other parts of the high pressure fuel system malfunction, the high pressure pump can be deadheaded (e.g., have no path back to the fuel tank) and can generate extremely high pressures at the output of the pump. The high pressures may even exceed the proof pressure of the system, resulting in catastrophic failure of hoses or seals in the high pressure fuel system of the engine.
Thus, there is a need for a high pressure fuel system which quickly supplies fuel to the engine as the engine is started. Further, there is a need for a high pressure fuel injection system which allows the feed pump to directly provide fuel to the engine. Additionally, there is a need for a high pressure fuel system which includes overpressure protection.